Sheet coating means with safety clutch



April 12, 1960 H. P. FRY, JR

SHEET comma MEANS WITH SAFETY CLUTCH Filed May 31, 1956 United States 2,932,276 SHEET COATING MEANS WITH SAFETY CLUTCH Horace P. Fry, Jr., West Chester, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware Application May 31, 1956, Serial No. 588,334

3 Claims. (Cl. 118-33) This invention relates to an apparatus for coating sheet material. More specifically it relates to an improved safety clutch and doctor roll combination for advancing 'a freshly coated cellophane sheet.

This case is a continuation-in-part of applicants copending application Serial No. 568,532, filed February 29, 1956. 1

The manufacture of cellophane sheet or film by the continuous extrusion of an alkaline viscose solution through a slit into an acid coagulating bath is well-known. The coagulated film is drawn from the coagulating bath through a series of treating baths wherein the film is successively regenerated, desulfurized, bleached, dyed if desired, and finally softened with plasticizer. To render the cellophane moisture-proof it is subsequently coated with a moisture-proofing lacquer by passage through a lacquer solution of, say nitrocellulose in a solvent such as acetone, toluene, or alcohol. drying of the lacquered sheet to expel the lacquer solvent and recover it for re-use. This general process is described in US. Patent No. 1,826,697. The present invention is an improvement in the means for advancing The final step is the Patented Apr. 12, 1960 or ce In present day operation of cellophane coating machines of the type described, the doctor rolls are rotated through a plate clutch actuated by compressed air. The plates have leather discs that press against a sprocket. When the air pressure is released the thrust on the sprocket is considerably reduced, though in many cases not sufficient to stop the rotation of the doctor rolls, which is necessary at certain times. Furthermore in order to rotate the doctor rolls with sufiicient reliability to give a good quality product, the plates are made extra large in order that suflicient torque is transmitted through the clutch. Because of the large torque necessary the arrangement is hazardous at times, as when an operator gets his arm caught between the rotating doctor rolls or when there is excessive wrapping of cellophane around them. There have been cases where the clutch did not slip sufficiently, and paper wound around the rolls to an extent where it actually bent 'the rolls and required overhauling of the machine.

The object of this invention is to provide a clutch for driving the doctor rolls which will transmit sufficient torque to give them a constant rotative speed, but which will disengage when the doctor rolls are overloaded due to excessive wrapping of cellophane, or other obstruction. Another object of the invention is to release the doctor rolls so that they are free wheeling and do not have any drag from the clutch, unlike present day arrangements.

Referring to Figure 2, doctor rolls 20, 20a, 20b, and

200 are rotatably supported at one end by bearings 25,

7 roll 20a is directly driven through the rotation of a the freshly coated sheet to the drier, employing a doctor roll mechanism to be described later and also. illustrated I taken along cutting plane 3-3 of Figure 2.

Referring to Figure 1, the film 5 to be coated may be a cellophane sheet which has been freshly cast and prehumidified to soften it and prepare it for coating. In one specific modification the sheet is 62-68 inches wide. The sheet 5 passes under a spreader roll 10, and over a rotating straight roll 11 disposed within an opening in the sidewall 13 of a coating head indicated generally at 17. Here it passes down through a lacquer pool 12, such as nitrocellulose, in dip pan 14, around a roller 15 immersed therein, and up between squeeze rolls 16, 16a and doctor rolls 20, 20a, 20b, and 20c into a drying zone not shown. The latter may be of the type described in applicants copending application Serial No. 568,532.

Squeeze rolls 16, 1611 are of hardened alloy steel, chrome plated, precision ground, and accurately positioned to limit the clearance through which the sheet 5 passes to about 2 /2 thousandths of an inch. Their function is to squeeze out excess lacquer from the sheet before it is dried. From rolls 16, 16a the sheet 5 passes between two pairs of small diameter doctor rolls 20, 20a, 20b, and 200 which are staggered so that the sheet describes a slight zigzag path in passing between them. Their purpose is to smooth out minute irregularities in the coating as it comes from the squeeze rolls. Each pair of rolls rotates counter to the direction of sheet travel at a surface speed the same as or less than that of the sheet.

the clutch I cup-like disc or element 35 keyed onto a shaft 36, which in turn is coupled to the doctor roll 20a through a nut a. The rotation of doctor roll 20a is counterclockwise to the direction of sheet travel, as indicated by the arrows at each end of the sheet 5, and in turn rotates attachedgear 75. Gear 75 meshes with pinions 76, 77 fixed to doctor rolls 20, 20b respectively, with the pinion 77 in turn rotating a gear 78 on the doctor roll 20c. Pinions 76, 77, and 78 are similar to gear 75, each being keyed to their respective doctor rolls and held in place thereon by nuts 76a, 77a, and 78a respectively. It is evident that in the gear train illustrated here pinions 76, 77 will rotate counter to the direction of gears 75 and 78. This means that the sheet 5 must be pulled forwardby means independent of the doctor rolls.

Referring to Figures 2 and 3, the driven member or disc 35 constitutes one member of a clutch, the driving member of which is a circular disc 37 having a journal 38 mounted in a bearing 40 and driven at constant speed through a member 41. Member 41 is secured to journal 38 by washer 42 and nut 43, the latter of which also serves to connect a conduit 45 with an inner bore or passage 46 in journal 38. Conduit 45 is in turn connected to an air line 47 through a rotary joint, while the passage 46 connects with three radial holes 50. With reference to Figure 3, it will be seen that engagement between the inner disc 37 and outer disc 35 is eifected by means of three plunger like pins .52 fitted within radial bores 54. Each of the pins 52 has a rounded end and points radially outward, with its base having a groove for holding an O-ring 55 to effect a pneumatic seal. A washer 56 is fixed at the outer end of the bore and holds one end of a compression spring 58, while the other end of the spring bears against the lower portion of the pin, forcing the same radially inward toward the center of the driving disc 37.

The inside diameter of the disc 35 is slightly larger than the outside diameter of the driving disc 37 and has. three or more radially-shaped grooves or notches 60.

As the pins 52, are pushed outwardly they will pop in and out of the groove 60 whenthe two members 35 and 37 turn at diflerent speeds. When no air pressure is applied to the pins they are in a declutched position, which means they have been pushed inward by the compression springs 58 as shown on the drawing;

Normally the driving disc 37 is rotating constantly. To engage the clutch mechanism with the doctor rolls, air under pressure is delivered through members 45 and 47 and passage 46 thereby pushing the pins 52 outwardly. The pins will pop into the radial grooves 60 and thereby cause the disc 35 to rotate. The disc 35 gradually picks up speed until both discs 35 and 37 are moving at the same rotative speed and at this stage all the pins 52 are seated within a radial groove 60. For most efiicient operation the pins 52 and grooves 60 are equally spaced so that all pins will be seated in grooves at the same time. The amount of driving torque to be transmitted can be controlled by the air pressure exerted on the pins. 7 i

In the normal operation of this mechanism the torque required to turn doctor rolls 20, 20a, 20b, and 200 as sheet advances therethrough will keep the pins 52 engaged with the outer clutch member 35. However when the doctor rolls encounter a resistance to rotation which exceeds the torque transmitted bythe clutch and associated driving means, pins 52 will pop out of grooves 60, thus effectively disengaging the outer and inner clutch members 35 and 37 without affecting the rotation of the latter. As stated above the sourceof-resistance may be an operators arm or a jam-up in the sheetS. In either case the doctor rolls are quickly stopped, even though the power flow from member 41 to disc '37 remains constant. When the stoppage'in-thedoctor rolls has been removed, as by the operator withdrawinghis arm, theouter clutch member 35 will be re-engaged by the pins 52 to resume the rotation of the doctor rolls.

The foregoing specification should be considered as illustrative, not limitative, since various modifications can be made in the apparatus without departing from the spirit of the invention. While the clutch mechanism per se is somewhat analogous to that described in U.S. 2,443,593, its basic principle of operation is new, especially in the combination described herein and claimed below.

Iclaim:

1. Apparatus for coating a running length of sheet material including a container for fluid coating material, means for passing a running sheet material through the fluid coating material within said container, means for removing the excess coating material from the sheet material as it leaves said container, a plurality of sheet engaging cylindrical rollers disposed along opposite sides of its' path of travel, means for drawing the sheet material between said plurality of cylindrical rolls, means including a driving mechanism for rotating said rollers in a direction opposite to the travel of the sheet material to thereby smooth out wrinkles from the surfaces thereof-,,said last-mentioned means including a clutch designed to substantially disengage said rollers from said driving mechanism when said rollers are subjected to an abnormal resistance to rotation.

2. An apparatus as defined in claim 1 wherein said means'for rotating said rollers includes a train of meshing gears operatively connected with said-clutch,-with alternate gears of said train of gears being connected to rolls disposed on the same side of the path of travel of the sheet material.

3. Apparatus as defined in 'claim 1 wherein said clutch includes a cup-shaped disc operatively connected with said rollers, 21 plate connected with the driving mechanism and disposed within said cup-shaped'disc, a plurality of pins mounted for sliding movement radially of said plate, yieldable means urging said pins toward the axis of said plate, a source of fluid under pressure operatively connected with said pins for urging the same in an outward direction, and a plurality of arcuately spaced grooves formed along the internal wall of said cup-shaped disc, said grooves mating with said pins when the latter are urged in an outward direction to thereby engage the plate with said disc.

References Cited in the file of this patent UNITED STATES PATENTS 1,826,697 Charch etal Oct. 6, 1931 1,986,822 Johnson Jan. 8, 1935 2,157,574 Siesel May 9, 1939 2,443,593 Birsch June 22, 1948 2,511,518 Stephens June 13, 1950 2,600,327 Ridge June 10, 1952 

